a) Field of the Invention
The present invention relates to an image pickup device forming an object image on a solid-state image sensor through an objective lens.
b) Description of the Prior Art
Generally, in an image pickup device provided with an image pickup portion adapted to secure a picture signal by arranging regularly pixel elements on a light receiving surface to space-sample two-dimensionally an object image as in solid-state image sensors represented by CCD image sensors, MOS image sensors, etc., when fine stripe regularly arranged and the like is photographed, the stripes interfere with the pixel elements, in a regular disposition, of the solid-state image sensor (in other words, a spatial frequency part of the objective image beats sampling frequency of the image pickup image sensor) and thereby moire, that is, a rough stripe pattern is liable to be displayed on the screen of a TV monitor. Also, in an image sensor provided with a color stripe filter or a color mosaic filter in front of the light receiving surface thereof, if a high spatial frequency part of the spectrum such as a minute bright spot and a clear boundary between bright and dark portions is included in an object, the high spatial frequency part of the spectrum is folded into a frequency region less than Nyquist rate of the image sensor when such spot and boundary are picked up, and thereby, as shown in FIG. 2 (which shows the case where bright spots are provided in the object), the bright spots are displayed as false signals (the so-called aliasing) with colored trails 3 on the screen of a TV monitor 2. In order to eliminate these defects, an arrangement has been made in the past so that an optical low-pass filter comprising a quartz plate and the like is provided in front of a solid-state image sensor 4 shown in FIG. 1. However, various problems have arisen that the quartz plate is high in cost and the arrangement of the optical low-pass filter needs a large space in an optical system.